1. Field of the Invention
The present invention relates generally to an antennae system for a telecommunications system, particularly to an improved antennae system configuration.
2. Background and Objects of the Present Invention
The evolution of wireless communication over the past century, since Guglielmo Marconi's 1897 demonstration of radio's ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi's discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which time the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue to rise in the coming decades as well, as this wireless network interacts with and eventually overtakes the existing wireline networks.
In order to facilitate the rapid expansion of cellular and other wireless telephonic uses there is a need for an improved infrastructure of reception and transmission apparatus to handle the increasing load and provide better coverage. More particularly, there is a need for an improved antennae system configuration at a base station node.
Shown in FIG. 1 is an example of an antennae system 10 presently in use. The antennae system 10 has two spaced-apart antennae clusters 12A and 12B, each having six antennae numbered 14A-14F, as illustrated. The individual antennae in one cluster are paired with the corresponding antennae in the other cluster, e.g., antenna 14A.sub.1 in cluster 12A is paired with antenna 14A.sub.2 in cluster 12B, as illustrated. Further, the six individual antennae within each cluster are mounted side-by-side to provide omni-directional coverage, e.g., 6 geographical sectors of 60 degrees each. It should be understood that a given antenna pair, e.g., antennae 14A.sub.1 and 14A.sub.2, may constitute a part of a base station transceiver for mobile radio frequency (RF) telecommunication.
With reference also to FIG. 2, antennae clusters 12A and 12B are mounted on poles 16A and 16B, respectively, of a crossbar or support 16. As illustrated, antennae clusters 12A and 12B are both horizontally and vertically spaced apart. As is understood in the art and as will be discussed more fully hereinafter, such spatial separation between antenna pairs is necessary to achieve diversity gain, i.e., an increase in reception capability, allowing a reduction in received signal power for the same performance. As shown in FIG. 1, antennae diversity in this conventional configuration is achieved by spatially offsetting an antenna pair, e.g., the aforementioned antenna 14A.sub.1 in antennae cluster 12A and the corresponding pair element 14A.sub.2 in antennae cluster 12B. In the Ericcson DECT Radio Access (DRA1900) System, for example, which uses a configuration similar to that illustrated in FIGS. 1 and 2, antennae clusters 12A and 12B are horizontally offset by approximately 2 meters and vertically offset by about 1 meter. The actual separation distance, computed using the Pythagorean theorem, is approximately 2.23 meters, the horizontal component being dominant.
Several technological disadvantages of the antennae construction 10 of FIGS. 1 and 2 are apparent, however, which are eliminated or ameliorated by the configuration of the present invention, described hereinafter. First, the antennae construction 10 is mechanically unbalanced, particularly with regard to wind load, increasing the chance of mechanical failure. Second, in one direction, i.e., along one or two of the geographical sectors of coverage, one cluster shadows the other, reducing the diversity gain. For example, antennae cluster 12B shadows at least a part of the coverage of antennae 14B.sub.1 and 14C.sub.1 in antennae cluster 12A. Diversity gain is also adversely affected by the unequal length of antenna cables (not shown) to the respective antennae clusters 12A and 12B. As is understood in the art, if the cables are unequal in length, there is unequal cable loss (dB) between the two antennae clusters, unbalancing the radiated power of the respective antennae 14 and reducing the diversity gain. An additional problem is horizontal separation variance. Since horizontal antennae separation in most propagation environments is more effective than vertical separation and is therefore the main contributor to diversity gain, to maximize such gain, particularly in the horizontal or azimuthal plane, the horizontal separation should be between about 2 to 4 meters to achieve about 10dB in diversity gain. Distances below about 2 meters have greatly reduced effectiveness with almost all diversity gain lost at about 1 meter separation. Distances beyond this range generally do not add to the approximately 10dB in gain, and become mechanically complex when larger than about 4 meters. Conventional antennae apparatus vary this horizontal distance somewhat, particularly, by providing spacing outside this optimum range, thereby either losing the benefits of diversity gain or wasting space.
As a result of the aforedescribed horizontal separation variance and shadowing due to the configuration of the mechanical support structure, the diversity gains in conventional antennae systems 10 vary accordingly. More particularly, diversity gain varies as a function of the angle between a first line drawn from the base station, i.e., an antenna pair discussed hereinafter, to the mobile subscriber or other wireless unit and a second line drawn between the two antennae clusters 12A and 12B. Thus, in existing antennae systems, such as those employing the configuration illustrated in FIGS. 1 and 2, diversity gain is not constant over the full 360 degrees. Further, the coverage area shape may be distorted, complicating cell planning. Lastly, since the mechanical support structure is unbalanced, additional costs and complications are added to antennae site construction.
It is in light of this background information related to antennae configuration and support structures that the significant improvements of the present invention have evolved.
It is, accordingly, an object of the present invention to provide an improved antennae support structure that overcomes or reduces the aforedescribed disadvantages of presently existing systems.
It is a more particular object of the present invention to provide a more balanced and structurally symmetric antennae system.
It is also an object of the present invention to provide an antennae system which maximizes diversity gain, and provides improved geographic uniformity in area coverage.